1. Technical Field
The present invention relates to an image reading apparatus and an original holder of the same.
2. Related Art
An image reading apparatus such as a scanner is provided with an image sensor for reading images from an original. Such an image sensor is provided with a plurality of photoelectric conversion elements such as a photodiode, and these photoelectric conversion elements generate electric charges in an amount corresponding to the amount of light received. Images are read by detecting this electric charge amount (see JP A-10-276305 and JP A-10-276368).
However, image sensors may have a following problem, that is, when electric charges generated by photoelectric conversion elements are transferred to a detection section to detect the amount of the electric charges, part of the electric charges may remain in a transfer path or the like, and all the electric charges may not be transferred to the detection section.
This type of problem is called a “linearity defect”. When the linearity defect occurs, in the read image, a defective image streak appears in a portion of which a photoelectric conversion element subject to the linearity defect takes charge. As a result, the read image becomes inadequate.
Accordingly, inspecting the linearity defect is examined as one of pre-shipment inspections at the manufacturing line of the image forming apparatuses. If a photoelectric conversion element subject to the linearity defect is found, the positional information of such a photoelectric conversion element is stored in a memory or the like of the image forming apparatus. When an image is read by a user after shipment, read data based on the photoelectric conversion element subject to the linearity defect that is identified by the positional information is not used, and instead, the data corresponding to the position is generated by interpolation using the read data of the photoelectric conversion elements that are located on both the adjacent sides of the photoelectric conversion element subject to the linearity defect so as to compensate for the defective image streak.
However, the occurrence of the linearity defect is temperature-dependent, and therefore even a photoelectric conversion element that had a favorable evaluation in the pre-shipment inspection at the manufacturing line may cause the linearity defect depending on the use temperature environment after shipment. In other words, it is considered that specifying photoelectric elements that may cause a defective image due to the linearity defect without fail is difficult only by the pre-shipment inspections.